对象引用 NSCopying 代理
.h
@interface xk : NSObject <NSCopying> @property (nonatomic, copy) NSString *string1;
@property (nonatomic, copy) NSString *string2
@end
实现代理【拷贝】方法
.m
- (id)copyWithZone:(nullable NSZone *)zone {
xk *xk1= [[[self class] allocWithZone:zone] init];
xk1.string1 = [self.string1 copy];
xk1.string2 = [self.string2 copy];
return xk1;
}